James F. McGrath has an interesting post entitled, "The Trinity Debate and John 17:3." In it, he responds to a rather convoluted, eisegesis-driven approach by a Trinitarian on John 17:3:
First, what John 17:3 actually says is perfectly consistent with the doctrine of the Trinity. Trinitarianism affirms that the Father is the only true God. After all, if there is only one true God, and the Father is God, then the Father must be the only true God. It is also consistent with the Trinity to affirm that the Father sent Jesus Christ.
So what’s the problem? Anti-Trinitarians think that the sentence creates a disjunction between “the only true God” and “Jesus Christ,” implying that Jesus Christ is not the only true God. But this is not quite correct. John 17:3 does distinguish between the Father (“you”) and “Jesus Christ,” and in this same statement identifies the Father as “the only true God,” but the statement does not deny that Jesus Christ is also true God. Rather, Christ is honoring the Father as the only true God (which he is!) while trusting the Father to exalt him at the proper time. Thus, Jesus immediately goes on to affirm that he had devoted his time on earth to glorifying the Father (v. 4) and to ask the Father in turn to glorify him (v. 5).
If John 17:3 did mean that the Father was the only true God to the exclusion of Jesus Christ, then it would be odd for John in other passages to affirm that Christ is God. If there is only one true God, and Jesus is not that God, then he is not truly God at all. Yet John explicitly calls Jesus “God,” and does so in contexts that make it clear that he is God no less than the Father.
McGrath correctly notes:
Apart from the convoluted attempt to claim that John 17:3 means something other than what it appears to, the above argument completely ignores the ways in which “God” is used more broadly in the Judaism of this time. Angelic figures were referred to as “gods” by Jews who would have spoken of one alone as “the only true God,” while Philo in particular distinguishes between one alone who is rightly called God, while the Logos is referred to as God in a lesser sense, by extension. John fits quite naturally into that first-century Jewish context, and to ignore that context in order to make John seem to be an advocate for later theological formulations seems an inappropriate (not to mention irreverent!) way of using the text. To make the argument that any use of theos must mean “God in the same sense as the Father is God” not only ignores but contradicts the sources we have from the time period in which this Gospel was composed.
I would highly recommend McGrath’s two books, The Only True God: Early Christian Monotheism in Its Jewish Context and John's Apologetic Christology: Legitimation and Development in Johannine Christology for a good, scholarly discussion on the issue of New Testament theology on these points.